1. Field of the Invention
The present disclosure relates to a correction method, more particularly, to a method of utilizing a spatial geometric calibration to improve the accuracy of lens distortion correction.
2. Description of the Related Art
Common optical apparatuses use optic lenses for forming image, such as an image capture device. In image capture device, light transmits to the charge coupled device via optic lenses for forming image. The image forming depends on the optic lenses, so the design of the optic lenses affects the quality of a formed image directly.
The image capture device which forms image by the optic lenses has problem of chromatism and distortion in formed image. There are two typical distortion types. First distortion type is barrel distortion, the four side edges of the formed image is protrusive outward, compared to four corners. The other type is a pincushion distortion, the four side edges of the formed image is concave inward, compared to four corners. Due to the deformation cause by the optic lenses, the image of two parallel straight lines has various intervals at different imaging positions.
The deformation caused by the optic lenses makes the equal intervals between potions or lines become non equal on the image, so the image distortion occurs.
Basically, the image distortion has point symmetry with respect to the image center, and most image coordinate transformation relationships for correcting the deformed image include an image center parameter. Ideally, the lens center must be located on a normal line from the center of an image sensor unit in assembly of the optical lens and the image sensor unit, and the distortion causes the optic lenses can have point symmetry with respect to the image center of the image.
However, in practical assembly, the optic lens center is usually not located on the normal line from center of the image sensor unit due to tolerance of the optic lenses or fault occurred in assembly flow. Therefore, the distortion caused by the optic lenses cannot have point symmetry with respect to the image center of the image, and it makes the accuracy of correction decrease.